.enlarge_box {
    width: 380px;
    position: relative;
}

.enlarge_box>.show {
    width: 380px;
    height: 400px;
    position: relative;
    text-align: center;
    cursor: move;
}

.enlarge_box>.show>img {
    width: 100%;
    height: 100%;
}

.enlarge_box>.show>.mask {
    width: 200px;
    height: 200px;
    background-color: yellow;
    opacity: .4;
    position: absolute;
    top: 0px;
    left: 0px;
    display: none;
}

.enlarge_box>.enlarge {
    /* 容器 与背景图的比例为 1 ：2 */
    width: 400px;
    height: 400px;
    position: absolute;
    top: 0px;
    left: 380px;
    background-size: 800px 800px;
    background-position: 0 0;
    background-repeat: no-repeat;
    border: 1px solid #eaeaea;
    background-image: url(../images/1234.jpg);
    display: none;
}